Rotary Instruments in Operative Dentistry

Rotary Instruments in Operative Dentistry

2. Dr. Nithin Mathew

3. CONTENTS

+ Rotary Abrasive Instruments
Diamond abrasives

Factor affecting abrasive efficiency
Other abrasives:

+ Molded

+ Coated

+ Introduction

+ History of Rotary Instrumentation
+ Powered Rotary Instruments

+ Rotary cutting Instruments

+ Common design characteristics
+ Bur Classification systems

+ Modifications in bur design + Cutting Mechanisms

+ Factors influencing cutting + Evaluation of Cutting
efficiency of burs + Bladed Cutting

+ Abrasive Cutting

+ Cutting Recommendation

rative Dentistry - Dr. Nithin Mathew

4. + Hazards with rotary instruments
+ Pulpal Precautions
+ Soft tissue precautions
+ Eye precautions
+ Ear precautions
* Inhalational precautions

+ Infection Control & Sterilization
Recent Advances
Conclusion

itive Dentistry - Dr. Nithin Mathew

5. Introduction

+ Removal and shaping of tooth structure is an essential part of restorative dentistry.

+ Initially this was a difficult process accomplished entirely by the use of hand instruments.

+ In order to perform the intricate and detailed procedures associated with operative
dentistry, the dentist must have a complete knowledge of the purpose, availability and
application of the many instruments required.

rative Dentistry - Dr. Nithin Mathew

6. History of Rotary Instrumentation

Development
Hippocrates described a drill driven by chord around the shaft
Hand rotated instruments

First rotary instrument was introduced by Dr. Jonathan Taft
and called them “bur drills”.
Drill - rotated in either direction to perform cutting action.

Morrison - dental foot engine 700
Electrical dental engine 1000
Belt driven handpiece

Electrical engine was incorporated into the dental unit 5000
Diamond abrasive points were introduced 5000
Old units upgraded speed 10,000
Tungsten carbide burs 12,000

Walsh and Symmons - removal tooth structure with diamond 70,000
points

ments in Operative Dentistry - Dr. Nithin Mathew

7. Development
Ball bearing hand pieces
Water turbine hand piece
Belt driven contraangle handpiece (Page-Chayes)
Air- turbine angle handpiece
Air- turbine straight handpiece
Experimental air bearing handpiece

Contemporary air turbine handpiece

Speed
25,000
50,000
1,50,000
2,50,000
25,000
8,00,000
3,00,000

8. + Rotary instruments includes:

+ Hand Pieces
+ Burs
+ Polishing instruments

Nithin Mathew

9. Handpieces

* Classified according to their driving mechanism

+ GEAR driven handpiece \ >>

+ Rotary power is transferred by a belt which runs from an electric
| engine

+ Power is transfered from the straight handpiece by a shaft and gears
inside the angle section.

+ Capable of working at variable speeds though they work best at low

speeds

iments in Operative Dentistry - Dr. Nithin Mathew

10. + WATER driven handpiece
+ Discovered in 1955
+ Operate at speeds of 1,00,000rpm
+ Water is transported at high pressure to rotate the turbines
+ Quite in nature and highest torque

+ BELT driven handpiece

+ Introduced in 1955

+ Operate at speeds >1,00,000rpm

+ Excellent performance and great versatility

\IR driven handpiece
* Introduced in 1957
* Operate at speeds of approx. 3,00,000rpm

rative Dentistry - Dr. Nithin Mathew

10

11. Type of Handpiece

+ STRAIGHT handpiece
+ Long axis of bur lies in same plane as long axis of handpiece
+ Used in oral surgery and lab procedures.

+ CONTRA-ANGLED handpiece

+ Head of the handpiece is first angled away from and then back towards
the long axis of the handle

Because of this design, bur head lies close to long axis of the handle of
handpiece which improve accessibility, visibility and stability of
handpiece while working.

itive Dentistry - Dr. Nithin Mathew

11

12. + CONTRA-ANGLED handpiece

i. Air-Rotor Contra-angle handpiece

+ Gets power from compressed air supplied by the
compressed

+ Handpiece has high speed and low torque

ii. Micromotor handpiece
+ Gets power from electric motor or air-motor

Has high torque and low speed

erative Dentistry - Dr. Nithin Mathew

12

13. Speed Ranges in Rotary Instruments

+» Rotational speed of an instrument is measured in revolutions per minute

+ According to Sturdevant:
+ Low speed
+ Medium/Intermediate speed
+ High / Ultra high speed

ls According to Charbenau:

k _* Conventional/Low speed
+ Increased / high speed

+ Ultra high speed

:rative Dentistry - Dr. Nithin Mathew

:< 12,000 rpm
: 12,000 - 2,00,000 rpm
:>2,00,000 rpm

:< 10,000 rpm
: 10,000 - 1,50,000 rpm
:>1,50,000

3

14. + According to Marzouk:

+ Ultra low :300 - 3,000 rpm

+ Low : 3,000 - 6,000 rpm

+ Medium high : 20,000 - 45,000 rpm

+ High : 45,000 - 1,00,000 rpm
+ Ultra high :>1,00,000 rpm

_ + According to Clearance L. Sock (DCNA 1971):

+ Low/ Conventional :< 6,000 rpm

+ High / Intermediate : 6,000 - 1,00,000 rpm
+ Ultra / super speed :>1,00,000 rpm

rative Dentistry - Dr. Nithin Mathew

15. Speed is proportional to the rotational speed and the diameter of the instrument.

Low speed cutting is ineffective, time consuming and requires relatively heavy force
application.

Results in heat production and vibration of low frequency and high amplitude.

Heat and vibration are the main sources of patient discomfort.

At low speeds, burs roll out of the tooth preparation.
Carbide burs are easily broken at low speeds due to their brittle nature of the blades.

Low speed mainly used for cleaning teeth, occasional caries excavation, finishing and
polishing procedures.

:rative Dentistry - Dr. Nithin Mathew

15

16. + At high speeds, the surface speed needed for efficient cutting can be attained by use of
smaller and more versatile cutting instruments.

+ Advantages of high speed includes:

+ Diamond/carbide instruments remove tooth structure faster with less pressure,
vibration and heat generation.

+ No. of rotating cutting instruments required is reduced because smaller sized are
more universal in application.

+ Operator has better control and greater ease of operation

+ Instruments last longer.

+ Patients are less apprehensive as the operating time is reduced.

:rative Dentistry - Dr. Nithin Mathew 16

17. Color Coding for handpieces based on speed:

+ Coding indicates the relative gear ratio of each component and are present in
the form of dots / rings :

+ Blue : No change in speed
+ Green : Speed Reduction
iF + Red : Speed increase

erative Dentistry - Dr. Nithin Mathew. 17

18. Rotary Cutting Instruments

+ These are individual instruments intended for use with handpieces and are available in
various shapes and sizes.

+ Common design characteristics
+ Bur classification systems
+ Modification in bur design

erative Dentistry - Dr. Nithin Mathew

18

19. COMMON DESIGN CHARACTERISTICS

+ Each instrument consists of 3 parts:
+ Head
+ Neck
+ Shank

iments in Operative Dentistry - Dr. Nithin Mathew

19

20. SHANK DESIGN

+ Part that fits into the hand piece, accepts the rotary motion from the handpiece

Provides bearing surface to control the alignment and concentricity of the instrument.

+ Shank design and dimensions vary with the hand piece for which it is intended for.

ADA Specification No. 23 for dental excavating burs includes 5 classes

rative Dentistry - Dr. Nithin Mathew 20

21. 1. Straight hand piece shank

+ Shank portion : cylindrical, held by a metal chuck that accepts a
range of shank diameters.

+ Straight handpiece are now used for finishing and polishing
completed restorations.

rative Dentistry - Dr. Nithin Mathew

2a

22. 2. Latch-type handpiece shank

+ Complicated shape of this shank reflects the mechanism by which these
are held in the hand piece.

+ Shorter overall dimensions - permits easy access to posterior regions
in mouth.

+ Handpiece has a metal tube within which the instrument fits

erative Dentistry - Dr. Nithin Mathew

22

23. Posterior portion of shank is flattened on one side, end fits into a
D-shaped socket at the bottom of the bur tube.

Retained by a latch that slides into D-shaped socket

Used in slow and medium speed.

Small amount of wobble due to the clearance between instrument
and bur tube - controlled by the lateral pressure during cutting
procedures.

erative Dentistry - Dr. Nithin Mathew

23

24. 3. Friction-grip shank design

+ Developed for its use in high speeds.

+ Overall dimensions are smaller thus increasing access in posterior
teeth.

+ Simple cylinder manufactured very close to dimensional
tolerances.

+ Designed to be held in handpiece by friction between the metal
chuck.

rative Dentistry - Dr. Nithin Mathew

25. + Minor variations in shank diameter can cause substantial vibration
in the instrument performance and problems with insertion,
retention and removal.

rative Dentistry - Dr. Nithin Mathew

26. NECK DESIGN

+ Portion that connects the head to the shank.

+ Neck normally tapers from the shank to the head.

+ Main function - transmit rotational and transitional force to head.

+ Also provides visibility and ease of operation.

For this reason neck diameter is a compromise between strength and improved access
and visibility.

Operative Dentistry - Dr. Nithin Mathew

27. HEAD DESIGN

+ It is the working part of the instrument - cutting edges or points.

+ Shape and material used in manufacture are closely related to its intended application
and technique of use.

+ Head design forms the basis of instrument classification, such as; bladed instrument or
abrasive instrument.

erative Dentistry - Dr. Nithin Mathew

28. MATERIALS used in Manufacture of burs

+ Steel Burs

First developed burs

+ Designed for slow speed <5,000 rpm, dull rapidly at high speeds.
+ They are cur from steel blanks parallel to the long axis of the bur.
+ Bur is then hardened to VHN 800.

Once they are dulled, cutting efficiency is reduced, increasing heat and vibration.

rative Dentistry - Dr. Nithin Mathew 28

29. + Tungsten Carbide Burs

+ Manufactured by metallurgical process, by alloying powder of tungsten carbide with
powder of cobalt-nickel under pressure and sintered in vaccum.

+ Ablank is then formed and a diamond cutter is used to form the head design.

+ Has a VHN in the range of 1650 - 1700.

Perform better than steel burs at all speeds, superiority is greatest at high speeds.

rative Dentistry - Dr. Nithin Mathew

29

30. + Harder than steel, so does not dull rapidly.

+ Carbide is more brittle and more susceptible to fracture when subjected to sudden blow.

+ Most carbide heads are welded or brazed to a steel shank and neck.

rative Dentistry - Dr. Nithin Mathew

30

31. BUR CLASSIFICATION SYSTEMS

Classification systems developed by FDI & ISO to use separate designations for
shape head and head diameter, measured in tenths of amm.

SHAPES:
>Round:
+ Spherical

+ Used for initial tooth entry, extension of preparation,
preparation of retention features and caries removal.

Nithin Mathew

31

32. > Inverted cone:
+ Portion of a rapidly tapered cone with apex towards the neck.
+ Head length is same as diameter.
+ For providing undercuts in tooth preparation.

> Pear shaped:

+ Portion of a slightly tapered cone with small end of the cone
directed towards the bur shank.

+ Head length is same as diameter.
+ For providing undercuts in tooth preparation.

+ End of head may be continuously tapered or may be flat with
rounded corners.

+ Used in
+ Normal length : Class I tooth preparation for gold foil

+ Long length : for amalgam preparations
Nithin Mathew

32

33. > Straight Fissure:
+ Elongated cylinder
+ Used for amalgam preparations.

> Tapered Fissure:
+ Head tapered away from the shank
+ Used for indirect restorations

ind Cutting Bur:

+ For carrying out preparations apically without
axial reduction

Dentistry - Dr.

33

34. CLASSIFICATION

+ According to Mode Of Attachment to handpiece
+ Latch type
- Friction type

+ According to Composition
+ Stainless steel

+ Tungsten carbide

+ Combination of both

rding to their Motion
+ Right bur : clockwise

+ Left bur : anti-clockwise

rative Dentistry - Dr. Nithin Mathew

34

35. + According to their Length + According to their Shape

* Long + Round
+ Short + Inverted cone
+ Regular + Pear shaped
+ Wheel
+ According to their Use + Tapering fissure
+ Cutting + Straight fissure
+ Finishing + End cutting bur

+ Polishing

-rative Dentistry - Dr. Nithin Mathew 35

36. Original numbering - 9 shapes and 11 sizes.
Y & Ya sizes were added later.

0.032 0.039 0.047 0.055 0.

08 (10) (1.2) (1.4)

3 4
14

36

37. Standard Bur Head Sizes—Carbide and Steel (1955-Present)

Cross-cut burs
: 500 was added

Head Diameters in Inches (mm)

Head 0.020 0.025 0.032 0.040 0.048 0.056 0.064 0.073 0.082 0.091 0.100 0.110 0.120 0.130
Shapes (05) (06) (0.8) (10) (1.2) (14) (16) (19) (21) (23) @5) (28) (20) @3)

34

900 was added

Rotary Insteuments in Operative Dentist

38. Names and Key Dimensions of Recommended Burs

ADA Size ISO Size
Number Number

A 005
2
4
—006
334
169

Manufacturer's
Size Number

329
330
330L

Head
Diameter
(mm)
0.50
0.60
1.00
1.40
0.45
0.60
0.90
0.90
0.70
0.80
0.80
1.20
1.60

Head
Length
(mm)
0.40
0.48
0.80
1.10
12
0.45
4.30
5.60
0.85
1.00
3.00
4.00
5.00

Taper
Angle
(degrees)

Shape

Round

Round

Round

Round

Inverted cone
Inverted cone
Tapered fissure
Elongated tapered fissure
Pear, normal length
Pear, normal length
Pear, long length
Tapered fissure
Tapered fissure

39. BUR DESIGN
+ Bur head consists of uniformly spaced blades with concave areas between them.
+ Normally a cutting bur has 6, 8 or 10 blades and a finishing bur has 12-40 blades.

+ Concave areas are called the chip/flute spaces.

+ Actual cutting of the bur takes place at the edge of the blade.

iments in Operative Dentistry - Dr. Nithin Mathew

40. Parts of a Bur head includes:
Bur Blade

+ Blade is a projection on the bur head which forms a cutting edge.

+ Each blade has 2 sides:
+ Rake face / blade face (surface of blade on leading edge)
+ Clearance face (surface of blade on trailing edge)

+ 3 important angles:
Rake angle

erative Dentistry - Dr. Nithin Mathew

41. — à

RAKE
Rake Angle ANGLE |
ue

Most important design characteristic of a blade.
Angle between the rake face and the radial line.

rake angle: when rake face trails the radial line
rake angle: when rake face is ahead of radial line
rake angle: when rake face and radial line coincide

For cutting hard, brittle materials, a negative rake angle
minimizes fractures of the cutting edge, increasing the tool
life.

Carbide burs have blades with slight negative rake angle
and edge angle of approx. 90°

Rotary Instfliments in Operative Dentistry - Dr. Nithin Mathew

- TO AXIS OF BUR y

4
ré
£
> r

OTATION

42. RAKE |

ANGLE | ¿TO
1
Blade Angle / Edge Angle ;

+ Angle between the rake face and the clearance face.

+ Increasing the edge angle, reinforces the cutting edge and
reduces the likelihood of the edge of the blade to fracture.

|
i

ROTATION

iments in Operative Dentistry - Dr. Nithin Mathew 42

43. Clearance Angle RAKE |

ANGLE |_.-TO

+ Angle between the clearance face and the work.

+ Primary Clearance angle: Angle the land makes with the
work

+ Secondary Clearance angle: Angle between the back of the
bur tooth and the work

+» Significance:

* Clearance angle provides a stop to prevent the bur edge
from digging into the tooth and provides adequate chip
space for clearing the debris.

>

ROTATION

angles cannot be varied independently.

increase in the clearance angle causes decrease in the
fle.

iments in Operative Dentistry - Dr. Nithin Mathew 43

44. Concentricty

+ Direct measurement of the symmetry of the bur

Ie. It measures whether the blades are of equal length or
not.

Runout

+ Measures the accuracy with which the tip of the blades pass
rough a single point when bur is moving.

it measures the maximum displacement of the bur head
rom its center of rotation

Operative Dentistry - Dr. Nithin Mathew

45. Runout occurs if:
* Bur head is off center on the axis of bur
+ Bur neck is bent
+ Bur bur is not held straight in handpiece chuck

Runout causes:
+ Increased vibration during cutting
+ Causes excessive removal of tooth structure.

erative Dentistry - Dr. Nithin Mathew

46. ADDITIONAL FEATURES IN HEAD DESIGN

Head Length
+ Long to reach full depth of preparation

| Taper Angle

i

+ Generate necessary occlusal divergence.

eck Diameter
» Small neck : weakening of instruments against lateral forces
ng neck : hampers visibility during preparation.

iments in Operative Dentistry - Dr. Nithin Mathew 46

47. Spiral Angle
+ Produces smooth wall.

+ In high speed, smaller angle is preferred to improve efficient
cutting.

Cross-cuts

+ Notches in the blade edges to improve cutting effectiveness at low
and medium speeds.

+ Crosscuts effectively increase both cutting pressure resulting from
tation and perpendicular pressure holding the blade edge
inst the tooth.

erative Dentistry - Dr. Nithin Mathew

47

48. + Each crosscut blade cuts, it leaves behind small ridges on the
tooth surface.

* Since notches of two successive blades do not line up with each
other, these ridges formed from one blade are removed by the
successive blade.

+ Athigh speeds, the contact of bur with the tooth is not continuous.

ere, high cutting rate of crosscut is maintained but the ridges are
tt removed. This leaves behind a rough cut surface.

erative Dentistry - Dr. Nithin Mathew

48

49. FACTORS AFFECTING CUTTING EFFICIENCY OF BUR
1. Rake Angle, Clearance Angle, Blade Angle
+ More positive rake angle, greater is the cutting efficiency.

+ However it has 2 major drawbacks:
i. Reduces the bulk of the blade - bur can easily curve, flatten or even fracture.

ii. Positive rake angle produces chip, that is larger and tends to clog the flutes
+ Negative rake angle has a smaller chip and moves away from the blade

Clearance angle eliminates friction between the cutting edge and the work and prevents
bur from digging into the tooth.

rative Dentistry - Dr. Nithin Mathew 49

50. + Increase in clearance angle reduces the blade angle, thereby decreasing the bulk of the
blade.

+ Increasing the blade angle reinforces the cutting edge and reduces chance of the blade
edge to fracture.

rative Dentistry - Dr. Nithin Mathew

51. 2. Spiral Angle and Crosscuts

+ Burs with small spiral angles are preferred at high speeds as
small angles produce more efficient cutting.

+ Crosscuts tends to reduce the total length of the bur blade that
is cutting at any one time.

+ This increases the force per unit area, and thereby reduces the
pressure required to initiate cutting.

rative Dentistry - Dr. Nithin Mathew

51

52. 3. Concentricity and Runout

+ Itis the direct measurement of the symmetry of the bur head.
+ An indication of whether one blade is longer than the other.

+ Runout is the maximum displacement of the bur head from the
axis of rotation.

+ Average clinically accepted runout is 0.023mm

Operative Dentistry - Dr. Nithin Mathew 52

53. 4. Heat treatment

+ Used to harden a bur made of soft steel
+ This process preserves the cutting edge and hardens the bur to improve its life.

5. Influence of load

+ Load signifies the force exerted by the dentist on the tool head and not that
pressure or stress induced in the bur during cutting.

Load or force exerted is dependent on the speed of the handpiece.

Slow Speed : 1000 - 1500 gm (1-2 pounds)
igh Speed : 60 - 120 gm (2-4 ounces)

rative Dentistry - Dr. Nithin Mathew 53

54. 6. Influence of speed

+ Ata given load, rate of cutting increases with increase in speed, but this increase
is not directly proportional.

+ There is also a minimum rotational speed for a given load below which the tool
will not cut.

7. Number of blades
+ No. of blades are restricted to 6-8.

+ Decreasing the no. of blades, increases the force on one blade and also increases
the size of the chip removed.

Also it tends to reduce the clogging tendency since the flute space is larger.

rative Dentistry - Dr. Nithin Mathew

54

55. + Major drawback of lesser no. of blades:

+ Tendency of bur tooth wear is more
+ Cutting life is reduced
+ Increased tendency for vibration

| 8. Design of Flute ends

° 2 types

+ Star-Cut Design : Flutes come together at a common
point on the axis of the bur

«Revelation Design : Flutes come together at two
junctions near the diametrical cutting edge.

+ Revelation design is more efficient in direct cutting

erative Dentistry - Dr. Nithin Mathew

Revelation

55

56. MODIFICATIONS IN BUR DESIGN

Modifications were seen with the introduction of high speed hand pieces.

+ 3 major changes includes:

+ Reduced use of crosscuts
+ Extended heads on fissure burs

_ ¢ Roundening of sharp tip angles

Nithin Mathew

56

57. + Reduced use of crosscuts

+ At high speeds, produce rough surface.
+ Newer burs have reduced no. of crosscuts.

+ Extended heads on fissure burs

+ Carbide fissure burs with extended head lengths 2-3 times those of normal tapered
fissure burs of similar diameter have high efficiency at higher speed with light pressure.

f + Roundening of sharp tip angles

+ Proposed by Markley & Sockwell

+ Such burs will result in lower stress in restored teeth
+ Burs last longer

rative Dentistry - Dr. Nithin Mathew 57

58. Diamond Abrasive Instruments

+ They have a greater clinical impact due to long life and effectiveness in cutting enamel and
dentin.

+ Introduced in United States in 1942 and was used popularly as grinding and finishing
agents.

Terminology:
+ Diamond instruments consists of 3 parts:

+ Metal blank
_ ¢ Powdered diamond abrasive
+ Metallic bonding material

erative Dentistry - Dr. Nithin Mathew 58

59. + Metal blank resembles a bur without blades
+» 3 parts: Head, Neck & Shank

+ Head of blank is slightly smaller than the final dimension of
the instrument head to accommodate for the thickness of
abrasive layer.

+ Neck gradually tapers from the shank to the head.

+ For large disk/abrasives, it may not be reduced below the
shank.

Diamonds maybe either natural or synthetic; that are crushed
to a powder of desired particles in size and shape.

erative Dentistry - Dr. Nithin Mathew

HEAD

NECK

SHANK

59

60. + These are held against the blank while it is being electroplated
with a metal.

+ Done in multiple layers to provide a continuous regeneration of
cutting surface as wear occurs.

Classification
Classified based on average particle size of the abrasive:

+ Coarse grit 2125-150 um
+ Medium grit :88-125 um
* Fine grit :60 - 74 um

+ Very fine :38 - 44 um

ments in Operative Dentistry - Dr. Nithin Mathew

60

61. + Larger particles - area for the particles is reduced and are widely placed.

+ During cutting, only a few particles come in contact with the tooth surface which increases
the pressure on each particle.

+ Resulting in rough surface

rative Dentistry - Dr. Nithin Mathew

61

62. Head shapes and sizes
Available in wide variety of shapes and sizes.

Because of their design which an abrasive layer over an underlying blank, the smallest
diamond instrument cannot be as small in diameter as the smallest of burs, but a wide
range of sizes are available for each shape.

Rotary Instgliments in Operative Dentistry - Dr. Nithin Mathew

62

63. FACTORS INFLUENCING THE ABRASIVE EFFECIENCY AND EFFECTIVENESS

1. Size of the abrasive particle

+ Larger the particle size, more deeper is the penetration on the surface of the work,
hence rapid removal of the material occurs.

- 2. Shape of the particle
+ Should be irregular in shape for greater efficiency.

Irregular particles - sharp edge
So cuts better than round smooth or cuboidal particles which have a flat edge.

rative Dentistry - Dr. Nithin Mathew 63

64. 3. Density of abrasive particles

+ Refers to the no. of abrasive particles per unit area.
+ High density : closely spaced
+ Low density : widely spaced

| + Therefore, greater force will be exerted on each particle with low density when
À the particles are widely spaced increasing grinding efficiency.

Coarse grit have low density compared to fine grit.

iments in Operative Dentistry - Dr. Nithin Mathew

65. 4. Hardness of abrasive particles

+ To be effective, hardness of abrasive particle should be greater than that of the
work.

5. Clogging of the abrasive surface

+ Clogging of debris between the spaces of the abrasive particles affects grinding
because this partially blocks the penetration of the abrasive particles into the
surface.

Clogging is enhanced when particles are close together.

of coolant washes away the debris and prevent clogging.

rative Dentistry - Dr. Nithin Mathew 65

66. Speed and Pressure

+ Usual cause of failure of abrasive instruments is when excessive pressure is
applied onto them to increase cutting efficiency at inadequate speeds.

+ This results in loss of diamonds decreasing their cutting efficiency.

perative Dentistry - Dr. Nithin Mathew

66

67. Other Abrasives

Many types of abrasive were used in addition to diamond instruments. Now
they are restricted to shaping, finishing and polishing restorations.

Classification

In these instruments, the head is composed of abrasive particles, held in a continuous
matrix of softer material.

idly divided as:
+ Molded instruments
+ Coated instruments

rative Dentistry - Dr. Nithin Mathew 67

68. MOLDED ABRASIVE INSTRUMENTS

+ Have heads that are manufactured by molding or pressing a
uniform mixture of abrasive around a roughened shank or by
cementing a pre-molded head.

+ Have much softer matrix and tends to wear with use thus
exposing fresh abrasive particles.

+ Rigid molded materials have rigid polymer or ceramic as their
matrix.

Mainly used for grinding and shaping procedures.

erative Dentistry - Dr. Nithin Mathew

68

69. + Soft molded instruments use flexible matrix materials like
rubber, which are used for finishing and polishing procedures.

+ Mounted head are termed as points / stones.

+ Unmounted discs / wheel stones are available which can be
attached to a mandrel.

erative Dentistry - Dr. Nithin Mathew

69

70. COATED ABRASIVE INSTRUMENTS

+ Mostly discs that have a thin layer of abrasive cemented to a
flexible base.

+ Allows the instrument to conform to the surface contour of
the tooth or restoration.

+ Unlike molded instruments, coated instruments have to be
discarded when they wear off.

Used in finishing certain enamel margins/walls for indirect
restorations.

Most often for finishing procedures for restorations

rative Dentistry - Dr. Nithin Mathew

71. Materials Used

+ Matrix materials used are phenolic resins or rubber.
+ Some molded abrasives may be sintered or may be resin bonded.

+ Arubber matrix is flexible and allows ease of polishing.
+ Non- flexible rubber matrix is used for molded SiC discs.

_ Silicon Carbide ( Carborundum)

olded in forms of rounds, bud-shapes, wheels and cylinders of various sizes.

-green in color suited for fast cutting except on enamel.
moderately smooth surface.

rative Dentistry - Dr. Nithin Mathew 71

72. + Unmounted discs, popularly called as carborundum discs, are black or dark in colour.

+ They have a soft matrix and wear easily.
+ They produce moderately rough surface.

Aluminium Oxide

sed for the same instrument design as SiC.
ints are white, rigid, fine textured and less porous.

y produce smoother surface than SiC.

rative Dentistry - Dr. Nithin Mathew

73. Garnet (reddish) and Quartz (white)

+ Used for coated discs
+ Available in a series of particle sizes ranging from coarse to medium-fine.

+ Used for initial finishing.
+ Hard enough to cut tooth and other restorative materials except some porcelain.

Pumice

effectively but breaksdown rapidly.
d for initial polishing procedure.

rative Dentistry - Dr. Nithin Mathew

dered abrasive produced by crushing foamed volcanic glass into thin glass flakes.

73

74. Cuttlebone

.

Derived from cuttlefish
A soft white abrasive.
Used only in coated discs for final finishing and polishing.

It is so soft that it reduces the potential for tooth damage due to its abrasive action.

rative Dentistry - Dr. Nithin Mathew

74

75. Cutting Mechanisms

For cutting, it is necessary to apply some pressure so that the cutting tool will dig into
the surface.

The process of rotary cutting is complex and not completely understood.

1. Evaluation of Cutting

+ Cutting can be measured in both effectiveness and efficiency.

+ Cutting effectiveness is the rate of tooth structure removal (mm/min or mg/min).

Cutting efficiency is the percentage of energy actually producing the cutting.
It is reduced when energy is wasted as noise or heat.

rative Dentistry - Dr. Nithin Mathew 75

76. + Itis possible to increase effectiveness while decreasing the efficiency.

+ Te. In general both effectiveness and efficiency can be increased by increasing the speed.

2. Bladed Cutting

+ Tooth structure similar to other materials undergoes
brittle and ductile fracture.

+ Brittle fracture is associated with crack propagation,
usually by tensile loading.

Ductile fracture involves plastic deformation of the
material proceeding shear.

iments in Operative Dentistry - Dr. Nithin Mathew

76

77. Speed

+ Low speed - plastic deformation before tooth structure fracture
+ High speed - produces brittle fracture

Strain Rate

+ Faster the rate of loading, greater will be the strength, hardness, modulus of elasticity
and brittleness of the material.

+ For the blade to initiate the cutting action, it must be sharp, harder with high modulus of
elasticity than the material being cut.

This helps in exceeding the shear strength of the material being cut.

rative Dentistry - Dr. Nithin Mathew

78. 3. Abrasive Cutting

+ Similar to bladed cutting in many ways, but key differences result from the properties,
size and distribution of the abrasive.

+ Hardness of diamond provides superior resistance to wear and these particles tend to
have a very high negative rake angle.

+ When diamond particle cuts through a
ductile material, material will flow
laterally around the cutting point and
je left as a ridge of deformed material
mn the surface.

Operative Dentistry - Dr. Nithin Mathew

79. + Repeated deformation work hardens the distorted material until irregular portion become
brittle and breaks off.

+ This is less efficient than bladed cutting; therefore bur are preferred to cut through ductile
material like dentin.

‚Operative Dentistry - Dr. Nithin Mathew 79

80. + When diamond cuts through brittle material, most cutting results from tensile fractures
that produces subsurface cracks.

+ Hence they are most efficient to remove enamel than burs.

+ Also preferred for use in tooth preparations for bonded restoration, since they increase the
surface area.

iments in Operative Dentistry - Dr. Nithin Mathew

81. Cutting Recommendations

+ Requirements for effective and efficient cutting include using
+ Contra-angle handpiece
+ High operating speed
+ Air water spray for cooling
+ Light pressure
+ Carbide or diamond instrument

Carbide burs are better for end cutting, produce lower heat and have more blade edges per
iameter for cutting.

fective for punch cuts to enter tooth structure, intra-coronal tooth preparation, amalgam
oval, small preparations and secondary retentive features.

itive Dentistry - Dr. Nithin Mathew 81

82. + Diamonds are more effective than burs for both intra and extra coronal tooth preparation,
bevelling enamel margins and enameloplasty.

itive Dentistry - Dr. Nithin Mathew

83. Hazards with Rotary Instruments
Pulpal Precautions

+ Injury to the pulp caused by:
+ Mechanical vibration

+ Heat generation
+ Desiccation of the dentin
+ Transection of the odontoblastic process.

Pulpal sequelae, take 2 weeks to 6 months, depending on degree of trauma.

remaining tissue is effective in protecting the pulp in proportion to the square of its
kness.

83

rative Dentistry - Dr. Nithin Mathew

84. + Heat is produced by:

+ Steel burs than carbide burs
* Tools plugged with debris

+ Air-water spray must be used as

+ Acts as a coolant

_ + Moisten the tissues, lubricates

+ Cleans and cools the cutting tool thus increasing tool life
lear the operating site

rative Dentistry - Dr. Nithin Mathew

+ When used without a coolant, diamond abrasives > carbide burs.

84

85. Soft Tissue Precautions

+ Injury to lips, tongue and cheek.
+ Rubber dam used to isolate soft tissues

+ Use good accessibility and visibility to the operative field
+ Patient instructed not to make sudden movements.
+ If accident occurs, control haemorrhage with pressure pack

; Chance of mechanical pulp involvement during caries excavation is more with hand
‘uments than with rotary instruments.

ual caries can be removed using a bur at low speed and light intermittent forces.

itive Dentistry - Dr. Nithin Mathew 85

86. Eye Precautions

+ Use of protective eye wear
+ Eye damage from airborne particles
+ High volume evacuation is advised

Ear Precautions

+ High pitched sound by some air-turbine handpieces at high speeds.

Potential damage to hearing depends on:
+ Intensity or loudness (decibels- db)
+ Frequency (cps)

+ Duration of the noise

ceptibility of the individual

itive Dentistry - Dr. Nithin Mathew

86

87. + Increased age, existing ear damage disease and medications are other factors that can
accelerate hearing loss.

+ Air turbine handpieces at 30 pounds : 70 - 94 db at high frequency.

+ Noise levels > 75 db @ of 1000 - 8000 cps : hearing damage.
+ Protective measures are recommended for 85 db @ 300 - 4800 cps.
_ + Protection is mandatory at 95 db.
rk lugs, sound proof rooms with absorbing materials on walls and floor

i-noise devices can be used to cancel the unwanted sounds as well.

:rative Dentistry - Dr. Nithin Mathew

87

88. Inhalational Precautions

* Aerosols are fine dispersion in air of water, tooth debris, micro-organisms and / or
restorative materials.

+ Cutting amalgams or composite resin produce both sub-micron particles and vapours.

ace mask filters out bacteria and fine particulate matter
E not mercury or monomer vapours.

itive Dentistry - Dr. Nithin Mathew

89. Infection Control

+ Latch angles, burs and rotary stones must be cleaned & sterilized.

+ Handpieces are semicritical instruments requiring sterilization
+ Motor-end of micro-motor must be covered with a single used disposable plastic bag.

Scrub and disinfection of the end may also be performed

»rative Dentistry - Dr. Nithin Mathew 89

90. Sterilization of Burs

+ Presoak: burs placed in soap water to loosen debris
+ Cleaning: Stainless brush under water or ultrasonic systems

+ Sterilization by:
+ Dry-clave - 160°C for 30min
+ Autoclave - 121°C for 15min @ 15 lbs.

+ Tendency of corrosion at the neck region, hence soak in 2% Sodium nitrite prior to
autoclaving.

+ Chemiclave - chemical vapour under pressure: 131°C @ 20 pounds pressure.
+ Best suited for corrosion prone instruments.

rative Dentistry - Dr. Nithin Mathew go

91. Sterilization of Handpiece

+ With metal bearing:
+ Scrub the metal bearing with water and soap.
+ Lubricate and place in sterilization bag & autoclaved.

+ Lube-free ceramic bearing
+ Must not be chemically sterilized - damage to internal parts.

+ Chemical vapor pressure sterilization

thylene oxide gas
Provides both internal & external sterilization due to penetrating capacity.
'akes long time for sterilization.

r handpiece is generally not recommended

perative Dentistry - Dr. Nithin Mathew 91

92. Recent Advances

Single patient use burs:

+ Developed by CDC & ADA to minimise cross- contamination & prolonged sterilization
protocol

Turbo diamond:
+ Have diamond free zone or continual spiral of blank space.

+ The diamond free zone breaks surface contact with the tooth, thus allowing cooler &
cleaner cutting.

The continual spiral design leaves a smooth wall.

rative Dentistry - Dr. Nithin Mathew 92

93. Fiber-optic handpieces:
+ Provide light at the working site.
+ Shut off delay - allows illumination even after release at foot control

Cellular optic handpiece:
+ Handpiece can be repeatedly sterilized without light degradation.

ube free ceramic bearing handpiece:
Do not require lubrication
Care should be taken against chemicals

erative Dentistry - Dr. Nithin Mathew

93

94. Fissureotomy burs (carbide):
+ Tip of the bur is smaller than no. % round bur.
+ Helpful in conservative preparations

Smart Prep burs:
+ Aka Polymer bur / smart bur

+ Made from polymer

+ Self limiting

+ Effectively remove decayed dentin without affecting
the healthy dentin

rative Dentistry - Dr. Nithin Mathew

94

95. Conclusion

+ The introduction of rotary, powered cutting equipment was one of the truly major advances
in dentistry.

+ These advances have enabled us to move from operative dentistry to conservative dentistry.

+ Proper understanding of speed and its implication in clinical use will help in providing an
expertise treatment.

rative Dentistry - Dr. Nithin Mathew

95

96. References

+ Art & science of operative Dentistry - Sturdevant ( 4" Edition)

+» Art & science of operative Dentistry - Sturdevant ( 5% Edition)

+ Operative Dentistry - Marzouk
+ Textbook of Operative Dentistry - Vimal Sikri
+» Pickard’s Manual of Operative Dentistry (8' Edition)

xtbook of Operative Dentistry - Nisha Garg

rative Dentistry - Dr. Nithin Mathew

96

97. Rotary Instruments in Operative Dentistry - Dr. Nithin Mathew